Makassar Strait transport: Initial estimate based on Arlindo results

This report presents the initial evaluation of the transport and temperature of ocean water passing through Makassar Strait, which is the primary pathway of the Pacific to Indian Ocean transport called the Indonesian through-flow. The transport was measured as part of the Indonesian USA Arlindo program, by two moorings deployed within the Labani Channel, a deep constriction near 3 degrees S. Both moorings were operative from December 1996 to February 1998; the western most mooring operated until July 1998 The moorings were deployed during a weak La Nina phase. An El Nino condition began in March 1997, becoming extreme during the 1997 Summer and Fall, relaxing in early 1998 The Makassar thermocline depth and transport reflect the phases of ENSO. The thermocline was deeper during La Nina, when the warm pool of the tropical Pacific with its relatively high sea level and deep thermocline, is pressed zip against the Pacific entrance to the Indonesian Seas. A shallower thermocline occurs during Fl Nino when the warm pool shifts eastward in the Pacific Ocean, reducing its accessibility to the Indonesian seas. ENSO effects are also seen in the velocity data. As Fl Nino takes hold the deeper instruments recorded reduced speeds, as the throughflow shoals with the thermocline. The 1997 average Makassar Strait throughflow transport is 9.3 Sv (Sv = 10(6) m(3)/sec), assuming the flow in the upper 200 meters equals the flow measured by the current meter moored at 200 m. Other models for the surface flow range from 6.7 Sv (zero surface flow) to 11.3 Sv (thermocline shear is extrapolated to the sea surface). A comparison of the transports for the two December to February periods included in the records also reflects the ENSO effect: the transport during the El Nino months of December 1997 to February 1998 average 5 Sv, while the La Nina months of December 1996 to February 1997 averages 12 Sv, a 2.5 fold difference The Makassar transports determined from the Arlindo data are at the higher side of estimates based in Timer Sea and Indian ocean studies.